1. Field of the Invention
The invention relates to a process for preparing organosilicon compounds with phosphonate groups.
2. Description of the Related Art
Phosphonates can be prepared by the Arbuzov-Michaelis reaction (Ber. Dtsch. Chem. Ges. 1898, 31, 1048-1055; Pure Appl. Chem. 1964, 9, 307-335). In this reaction, haloalkanes or compounds which bear haloalkyl radicals are reacted with trialkyl phosphites. The preparation is effected in a batch process by mixing the reactants at high temperatures and subsequent distillation of the reaction mixture. In this way, it is also possible to prepare organosilicon compounds with phosphonate groups, referred to hereinafter as phosphonatosilanes, of the general formula (I),R1′n(R2′O)3-n—Si—R3′—PO(OR4′)(OR5′)  (I)in which R1″ is an optionally halogen-substituted alkyl, cycloalkyl, alkenyl or aryl radical, R2′ is an alkyl radical having 1-6 carbon atoms or an ω-oxaalkylalkyl radical having a total of 2-10 carbon atoms, R3′ is an optionally substituted, branched or unbranched alkylene radical having 1-10 carbon atoms, R4′ and R5′ are each an optionally substituted alkyl, cycloalkyl, alkenyl or aryl radical, and n=0, 1, 2 or 3 (U.S. Pat. No. 2768193; J. Polym. Sci., Part A: Polym. Chem. 2003, 41, 48-59). For the preparation of these compounds, temperatures of >170° C. are generally required. Since the compounds described, however, are of low thermal stability (J. Chem. Soc. 1962, 592-600) and decompose exothermically at temperatures of T≧200° C., the achievable yields are limited. Moreover, a not inconsiderable endangerment potential results therefrom. Particularly for compounds of the formula I in which R3 is a methylene unit, the preparation at reaction temperatures of T>100° C. is very problematic for safety reasons (100 K rule). When the reaction to prepare these compounds is conducted at reaction temperatures of T≦100° C., which presents fewer safety issues, the result is an uneconomic space-time yield.
The disadvantages of the known processes consist in the low space-time yields at low reaction temperatures and the restrictive yields at high reaction temperatures caused by the decomposition of the product, and the endangerment potential which originates from the exothermic decomposition reactions of the products.